This invention relates to the heat treating of metallic and non-metallic stocks in the form of strip, sheets, shapes and slabs, in both a continuous and batch type furnace, and more particularly to applying jet impingement technology and methods for heat treating stock.
The heat treating operation has drawn considerable attention over the last decade as higher energy cost, energy availability, operating cost, product quality and emission levels have come to bear. The need for high efficiency furnaces has resulted in efforts directed to achieve new levels of efficiency. Some of these efforts are reflected in Lazaridis et al. U.S. Pat. No. 4,202,661 entitled "Jet Implement Radiation Furnace, Method and Apparatus" which issued May 14, 1980 and Jayaraman et al. U.S. Pat. No. 4,373,702 entitled "Jet Impingement/Radiant Heating Apparatus" which issued Feb. 15, 1983.
The issues mentioned above have created a market need for high efficiency, less polluting furnaces. Though a considerable amount of effort and progress has been made, a new level of efficiency, temperature uniformity and emissions are necessary if industry is to continue to be competitive within the world market. This invention addresses the issues of higher efficiency, improved temperature uniformity and reduced pollutants.
Many existing industrial heat treating operations are productivity limited due to space constraints, quality requirements and temperature requirements. This invention offers an alternative solution to those limitations.
The newest heat treating furnaces are usually a continuous design where the stock is heated as it moves through the furnace. These furnaces incorporate convection heating, radiation heating or a combination of both. These furnaces are directed toward increasing energy efficiency. Likewise, many heat treating furnaces use various forms of jet impingement to increase the convective heat transfer rate and thereby improve efficiency within the furnace.
Many of the continuous heat treating furnaces using jet impingement require that the impinging source be in very close proximity to the workpiece in order to take advantage of the higher heat transfer rate. Likewise, this close proximity to the work makes maintenance more difficult and creates the opportunity for the stock to damage the furnace and its component parts as it travels through the furnace. Likewise, stoppage and/or slowdowns can result in loss of material due to poor quality resulting from non-uniformheating and/or not meeting energy rate requirements.
A primary object of this invention is to provide a zone controlled heat treating furnace that has high efficiency and produces less pollution by increasing the rate of the combustion reaction and by substantially increasing the convective heat transfer rate within the heat treating furnace.
A further object of this invention is to provide a heat treating and drying apparatus operable in either a heating and/or a cooling mode and having a control system to continuously monitor and select a mode whereby to precisely control the heating and cooling rates in these modes for improving product quality.
Another object of this invention is to provide a high pressure, high velocity, reacting mixture such that the distance to the workpiece is not critical. The high velocity/pressurized atmosphere also provides the ability to recover residual heat through a secondary heat exchanger and/or to remove unwanted substances from the flue exhaust.
Another object of this invention is to provide a plurality of like furnace burner modules which may be operatively connected in parallel to allow flexibility in design such that a wide variety of heat treating applications can benefit from the advantages of this process.
Another object of this invention is to provide a furnace having an elongated super atmospheric heating chamber through which workpieces are passed and which has a heat radiating surface encircling the path and through which high pressure/velocity flame or products of combustion will pass to impinge on the workpieces to generate a high convective heat transfer in a turbulent flow.
Yet another object of this invention is provision of a furnace to heat stock rapidly and provide uniform heating of the stock, even when the stock is of a complex shape. The high pressure/velocity and the high convective heat transfer rates coupled with a heating and/or cooling mode along with the flexibility to pattern and design the burner/jet nozzles based on the shape/configuration of the stock enables this system to meet this objective.
Still another object is to provide both a high convective heat transfer rate and a high radiation heating rate within the furnace environment and thereby maximize overall heat transfer within the furnace and reduce the cost to heat treat the stocks.
Yet another object of this invention is provision of a high pressure velocity combustion process to increase the rate of chemical reaction and reduce the rate of NO.sub.x formation over conventional burners.